how的用法可以灵活——
可以引导特殊疑问句，也可以用于名词性从句，还可以引导状语从句，也能使用从句的省略结构。例如
How are you getting on with your work?
I want to know how should I do it.
=I want to know how to do it.
当how从句主语和主句主语相同时，how从句中可以简化为how to do sth
His mother was always waiting for him no matter how late he went home.
